This invention relates to a two piece tapping or rethreading device and, more particularly, to such a device including at least a thread cutting member and a guide member which are inserted into the opening to be threaded and which cooperate with one another to cut threads in a work surface of the opening. The guide member presses against the cutting member during the cutting operation and thereby maintains the cutting means in proper alignment with the work surface and holds the cutting surfaces of the cutting member against the work surface.
Hand taps are a convenient means known to the art to cut internal threads in drilled holes. Conventional hand taps are comparatively short and have a thread cutting section and a shank of approximately the same length. The shank usually has a square end that accommodates a tap wrench or other turning device. The cutting area of a tap usually includes a plurality of flutes, with the cutting edges of the tap being on the raised sections that are on either side of a particular flute.
There are a number of different types of machine driven taps that have either a means of expanding or collapsing the cutting surface or tap chasers of a particular tap. Some adjustable taps of the expanding variety are made of a solid piece of metal which is split and provided with means for expanding the cutting surfaces to compensate for wear, while other types of adjustable taps have inserted blades or chasers which are rigidly held but are capable of radial adjustment.
Collapsing taps are used to collapse the tap chasers or cutting means of a tap in order to permit the rapid removal of the tap from a hole.
In each of the above types of taps, it is difficult to rethread damaged threads in a tapped opening because of the difficulty in aligning the good threads in the opening with the cutting edges of the tap. If the good threads are not properly aligned, the entire opening will be unnecessarily rethreaded and perhaps misthreaded.
Accordingly, it is an object of this invention to provide a simple and convenient means to align the good threads in a tapped opening with the thread cutting edges of the tap so that the tap may rethread only the damaged threads in the opening.
A further object of this invention is to provide means whereby a tapped opening may be rethreaded or a drilled opening may be initially tapped by the action of two separate tapping pieces cooperating with one another to tap or rethread the opening.
These and other objects of this invention will become apparent from a review of the detailed specification which follows and a consideration of the accompanying drawings.